What all is there to the extras? Manuals go without saying, but what approach do the walkthroughs take, and how's the quality of the artworks?

I'm just starting the first game, so I don't want to ruin anything for myself, but I did take a peek for ya.

The art work is a collection of 17 pieces of varying sizes, ranging from 650x748 up to about 2300x1200. A handful are concept sketches (Robot Arm, Antidote Machine, the Infected, and a Metal Bridge); the rest are full color art, but all are only 96 dpi and have a bit depth of 24.

There are only walkthroughs for two of the three games (Black Plague and Requiem). The one for Black Plague is a very basic here's-what-to-do-and-expect narrative, complete with typos. Requiem, however, looks better, has a nice little intro, and also has an "Alternative Solutions" section after each room's walkthrough.

Hope that helps!